The present invention relates to a centrifuge container for indirect cooling of materials in a laboratory centrifuge, or a laboratory centrifuge and a method for producing a centrifuge container for indirect cooling of materials in a laboratory centrifuge.
The present invention relates in particular to laboratory centrifuges, this means centrifuges which are used in chemical, biological, biochemical or biotechnological laboratories. On the other hand, the present invention can also be used advantageously for large scale centrifuges and mechanical stirring devices and for all devices in which a material has to be cooled at least indirectly. Thus, the invention can also be used for dedicated cooling devices, like e.g. refrigerators or freezers, in particular laboratory refrigerators or freezers, in which a very deep cooling shall be achieved. In such dedicated cooling devices, the container forms the housing of the interior of the device, into which the material is placed.
The invention in particular does not relate to cookware, frying pans or similar containers, which are used for heating materials, which can be disposed in the container.
During centrifuge operation, heat is generated during the rotation of the centrifuge rotor in the centrifuge container through air friction and electrical power dissipation. Since the centrifuge container is closed with a cover, in order to prevent the material to be centrifuged from exiting, this heat import cannot simply be removed and leads to an increase of the temperature of the material to be centrifuged.
This temperature increase, however, is mostly undesirable. Therefore, already in the past, measures were taken to avoid an increase of the temperature of the material being centrifuged. This can be performed through direct cooling or through indirect cooling through a heat exchanger principle. Thus, for indirect cooling, there is no direct contact between the cooling medium and the material to be cooled or the enclosure of the material to be cooled.
For direct cooling, the ambient air directly at the centrifuge rotor is conducted through the centrifuge container, wherein the rotor acts like a radial fan. Thus, the centrifuge cover and/or the centrifuge container comprise a recess close to the axis, and an outlet opening disposed more remote with respect to the axis of rotation. Though such a direct cooling has proven effective, the centrifuge container, however, has to have an outlet opening, which also facilitates material egress. Such containers thus cannot be used for stirring devices or similar, in which materials shall be directly mixed, and which thus have to be configured closed all around. Using the ambient air as a cooling medium is a disadvantage of the direct cooling method, since the material can only be cooled down to the temperature of the ambient air at the most.
For indirect cooling, the rotor is enclosed in the centrifuge container under the centrifuge cover, and no cooling channel or similar is provided. Thus, the air only circulates within the centrifuge container. Cooling is now facilitated through a second medium, which is conducted along the outside of the container. This can either be ambient air, which is conducted past the exterior of the container, as implemented e.g. for the centrifuge 5424 of Eppendorf AG. Or alternatively, a particular cooling medium is conducted along the container through pipes that contact the container, this means the side walls and the bottom plate of the container in a spiral, in order to remove heat. In the latter variant of the indirect cooling, also a cooling of the material to a temperature below the temperature of the ambient air is possible. An advantage of the indirect cooling is better controllability of the temperature to be controlled, compared to direct cooling.
The cooling effect that is obtained through indirect cooling, however, is not as efficient so far as for direct cooling, therefore the energy requirement for the same cooling power is accordingly high. This is a consequence of the limited surface contact of the cooling medium, which is conducted past the outside of the container.
Attempts are known in the prior art to improve indirect cooling. Thus, U.S. Pat. No. 5,477,704 A describes a centrifuge container with copper cooling coils glued to its outer side wall and its base plate with an aluminum filled epoxy resin. The aluminum filled epoxy resin has high heat conductivity and is used for supporting the heat transfer from the centrifuge container. The cooling coils disclosed in U.S. Pat. No. 5,477,704 A, which are glued to the container, have a particular configuration. The side of the cooling coil which contacts the side wall or the base plate is flattened in order to increase the contact surface between the cooling coil and the container. However, it is difficult to apply epoxy resin to copper coils and a certain curing time is required before such a container can be used or processed further. Additionally, the container and the interconnection epoxy resin/copper have different thermal expansion coefficients. This means that cracking noises can occur when the temperature changes, which give the user an uncomfortable feeling with respect to the operational safety of the centrifuge.
It is the object of the present invention to provide a container that facilitates efficient indirect cooling and which can be manufactured in a simple and cost effective manner. Furthermore, a device operating with the container and a method for producing the container shall be provided. Thus, the container shall not only be used in centrifuge applications, but also in stirring devices, cooling devices and similar.
Containers in the sense of the instant invention are all devices in which a material to be cooled can be disposed directly or indirectly through a separate enclosure, and can be cooled through indirect cooling through a cooling device that is in heat conducting contact. The container according to the invention can be configured with various outer shapes. It can be round or kettle shaped. In such case, the container comprises a round base plate from which a side wall rises at the outer rim. The upper side of the container can be closed through a cover that can be opened. In an alternative embodiment, the container has edges; this means it is configured rectangular or square. It then has a rectangular or square base plate from whose outer rim four respective side walls extend. The upper side of the container is closed by an upper plate. Depending on the use of the container, either at least one of the side walls is configured as a door that can be opened, or the upper side of the container, this means the upper plate, is configured as a cover that can be opened. When a “side wall” is recited infra, this that the term also includes the plural; this means “side walls”.